1. Field of the Invention
The present invention relates to a connection of a coupling collar to an end of a hardened conveying pipe.
2. Description of the Related Art
Single-layer pipes for fluidically (hydraulically or pneumatically) conveying solids, such as sands, gravels or concrete, have at least on the inside thereof a hardened surface in order to provide as high a wear resistance as possible to the usually very abrasive solids. As a rule, the higher resistance to wear is produced by flame hardening.
In addition, pipes of composite sheet metal are known, such as pipes of double-layer plated metal.
In order to be able to connect pipes of the above-described type to a pipeline, and to make possible an exchange of individual pipes from the otherwise closed pipeline, it is known in the art to equip the pipes at the ends thereof with coupling collars and to couple the pipes to one another in a releasable manner by means of these coupling collars. In order to ensure that the connection has a high tensile strength, the coupling collars are welded to the ends of the pipes. However, because of the influence of the heat, welding always leads to an unsatisfactory hardness at least at the pipe ends, independently of whether the pipes are hardened prior to welding to the coupling collars or after welding.
If hardening is carried out prior to welding, it is possible initially to achieve a uniform hardening of the pipes through the desired depth thereof. However, this uniform hardening is at least partially eliminated as a result of the influence of heat caused during welding of the coupling collars. If the pipes are hardened after welding the coupling collars to the pipes, the better heat discharge occurring in the areas of the pipe ends produces the result that the hardening is better in the middle portions of the pipes than in the end portions thereof. In both cases, the pipe ends are less resistant to wear than are the middle portions of the pipes. Accordingly, it is always necessary to completely replace the pipes, even though only the pipe ends are worn. The middle portions of the pipes would still have a much longer service life.
British Patent 998 253 and WO 93/16302 disclose glued connections.
The proposal according to British Patent 998 253 deals with a special connection of a coupling collar to an end of a pipe which on the inside thereof is provided with a light reflecting coating. Two of such pipes are to be connected to one another without a gap and in an exact axial alignment. For this purpose, initially the two pipes are exactly machined at the inside and outside thereof and are then coated with a light-reflecting inner coating. Subsequently, after sliding rings of adhesive material onto the pipe ends, the pipe ends are slid into the connecting pieces of two coupling collars whose inner surfaces are also exactly machined. This produces a very precisely defined joining gap. By means of measuring devices, the pipes as well as the coupling collars are now precisely axially aligned relative to each other while maintaining the joining gap having narrow tolerances, and the pipes and the coupling collars are clamped relative to each other in this aligned position. The clamped position is maintained until the adhesive has resulted in a secure connection of the pipe ends to the pipe connecting pieces of the coupling collars.
In this proposal, the service life of the light-conducting pipes is not a concern. The only concern is the precise connection of the coupling collars to the pipe ends in order to ensure a problem-free axial alignment of two successive pipes.
WO 93/16302 discloses a glued connection of gear wheels to one another and to a shaft. The glued connection is produced with a joining material while maintaining transition fits. The purpose is to prevent high residual stresses as they are known in shrunk-on connections.